Problem: Simplify the following expression: $k = \dfrac{3rs - 3ts}{6ts - 6s} + \dfrac{6ts - 6s^2}{6ts - 6s}$ You can assume $r,s,t \neq 0$.
Answer: Since the expressions have the same denominator we simply combine the numerators: $k = \dfrac{3rs - 3ts + 6ts - 6s^2}{6ts - 6s}$ $k = \dfrac{3rs + 3ts - 6s^2}{6ts - 6s}$ The numerator and denominator have a common factor of $3s$, so we can simplify $k = \dfrac{r + t - 2s}{2t - 2}$